text: /* Implementation helper: a struct that looks like a tuple.
     See timemodule and posixmodule for example uses.
  
     The structseq helper is considered an internal CPython implementation
     detail.  Docs for modules using structseqs should call them
     "named tuples" (be sure to include a space between the two
     words and add a link back to the term in Docs/glossary.rst).
  */
  
  #include "Python.h"
  #include "pycore_tuple.h"         // _PyTuple_FromArray()
  #include "pycore_object.h"        // _PyObject_GC_TRACK()
  #include "structmember.h"         // PyMemberDef
  #include "pycore_structseq.h"     // PyStructSequence_InitType()
  #include "pycore_initconfig.h"    // _PyStatus_OK()
  
  static const char visible_length_key[] = "n_sequence_fields";
  static const char real_length_key[] = "n_fields";
  static const char unnamed_fields_key[] = "n_unnamed_fields";
  static const char match_args_key[] = "__match_args__";
  
  /* Fields with this name have only a field index, not a field name.
     They are only allowed for indices < n_visible_fields. */
  const char * const PyStructSequence_UnnamedField = "unnamed field";
  
  _Py_IDENTIFIER(n_sequence_fields);
  _Py_IDENTIFIER(n_fields);
  _Py_IDENTIFIER(n_unnamed_fields);
  
  static Py_ssize_t
  get_type_attr_as_size(PyTypeObject *tp, _Py_Identifier *id)
  {
      PyObject *name = _PyUnicode_FromId(id);
      if (name == NULL) {
          return -1;
      }
      PyObject *v = PyDict_GetItemWithError(tp->tp_dict, name);
      if (v == NULL && !PyErr_Occurred()) {
          PyErr_Format(PyExc_TypeError,
                       "Missed attribute '%U' of type %s",
                       name, tp->tp_name);
      }
      return PyLong_AsSsize_t(v);
  }
  
  #define VISIBLE_SIZE(op) Py_SIZE(op)
  #define VISIBLE_SIZE_TP(tp) get_type_attr_as_size(tp, &PyId_n_sequence_fields)
  #define REAL_SIZE_TP(tp) get_type_attr_as_size(tp, &PyId_n_fields)
  #define REAL_SIZE(op) REAL_SIZE_TP(Py_TYPE(op))
  
  #define UNNAMED_FIELDS_TP(tp) get_type_attr_as_size(tp, &PyId_n_unnamed_fields)
  #define UNNAMED_FIELDS(op) UNNAMED_FIELDS_TP(Py_TYPE(op))
  
  
  PyObject *
  PyStructSequence_New(PyTypeObject *type)
  {
      PyStructSequence *obj;
      Py_ssize_t size = REAL_SIZE_TP(type), i;
      if (size < 0) {
          return NULL;
      }
      Py_ssize_t vsize = VISIBLE_SIZE_TP(type);
      if (vsize < 0) {
          return NULL;
      }
  
      obj = PyObject_GC_NewVar(PyStructSequence, type, size);
      if (obj == NULL)
          return NULL;
      /* Hack the size of the variable object, so invisible fields don't appear
       to Python code. */
      Py_SET_SIZE(obj, vsize);
      for (i = 0; i < size; i++)
          obj->ob_item[i] = NULL;
  
      return (PyObject*)obj;
  }
  
  void
  PyStructSequence_SetItem(PyObject* op, Py_ssize_t i, PyObject* v)
  {
      PyStructSequence_SET_ITEM(op, i, v);
  }
  
  PyObject*
  PyStructSequence_GetItem(PyObject* op, Py_ssize_t i)
  {
      return PyStructSequence_GET_ITEM(op, i);
  }
  
  
  static int
  structseq_traverse(PyStructSequence *obj, visitproc visit, void *arg)
  {
      if (Py_TYPE(obj)->tp_flags & Py_TPFLAGS_HEAPTYPE) {
          Py_VISIT(Py_TYPE(obj));
      }
      Py_ssize_t i, size;
      size = REAL_SIZE(obj);
      for (i = 0; i < size; ++i) {
          Py_VISIT(obj->ob_item[i]);
      }
      return 0;
  }
  
  static void
  structseq_dealloc(PyStructSequence *obj)
  {
      Py_ssize_t i, size;
      PyObject_GC_UnTrack(obj);
  
      PyTypeObject *tp = Py_TYPE(obj);
      size = REAL_SIZE(obj);
      for (i = 0; i < size; ++i) {
          Py_XDECREF(obj->ob_item[i]);
      }
      PyObject_GC_Del(obj);
      if (_PyType_HasFeature(tp, Py_TPFLAGS_HEAPTYPE)) {
          Py_DECREF(tp);
      }
  }
  
  /*[clinic input]
  class structseq "PyStructSequence *" "NULL"
  [clinic start generated code]*/
  /*[clinic end generated code: output=da39a3ee5e6b4b0d input=9d781c6922c77752]*/
  
  #include "clinic/structseq.c.h"
  
  /*[clinic input]
  @classmethod
  structseq.__new__ as structseq_new
      sequence as arg: object
      dict: object(c_default="NULL") = {}
  [clinic start generated code]*/
  
  static PyObject *
  structseq_new_impl(PyTypeObject *type, PyObject *arg, PyObject *dict)
  /*[clinic end generated code: output=baa082e788b171da input=90532511101aa3fb]*/
  {
      PyObject *ob;
      PyStructSequence *res = NULL;
      Py_ssize_t len, min_len, max_len, i, n_unnamed_fields;
  
      min_len = VISIBLE_SIZE_TP(type);
      if (min_len < 0) {
          return NULL;
      }
      max_len = REAL_SIZE_TP(type);
      if (max_len < 0) {
          return NULL;
      }
      n_unnamed_fields = UNNAMED_FIELDS_TP(type);
      if (n_unnamed_fields < 0) {
          return NULL;
      }
  
      arg = PySequence_Fast(arg, "constructor requires a sequence");
  
      if (!arg) {
          return NULL;
      }
  
      if (dict && !PyDict_Check(dict)) {
          PyErr_Format(PyExc_TypeError,
                       "%.500s() takes a dict as second arg, if any",
                       type->tp_name);
          Py_DECREF(arg);
          return NULL;
      }
  
      len = PySequence_Fast_GET_SIZE(arg);
      if (min_len != max_len) {
          if (len < min_len) {
              PyErr_Format(PyExc_TypeError,
                  "%.500s() takes an at least %zd-sequence (%zd-sequence given)",
                  type->tp_name, min_len, len);
              Py_DECREF(arg);
              return NULL;
          }
  
          if (len > max_len) {
              PyErr_Format(PyExc_TypeError,
                  "%.500s() takes an at most %zd-sequence (%zd-sequence given)",
                  type->tp_name, max_len, len);
              Py_DECREF(arg);
              return NULL;
          }
      }
      else {
          if (len != min_len) {
              PyErr_Format(PyExc_TypeError,
                           "%.500s() takes a %zd-sequence (%zd-sequence given)",
                           type->tp_name, min_len, len);
              Py_DECREF(arg);
              return NULL;
          }
      }
  
      res = (PyStructSequence*) PyStructSequence_New(type);
      if (res == NULL) {
          Py_DECREF(arg);
          return NULL;
      }
      for (i = 0; i < len; ++i) {
          PyObject *v = PySequence_Fast_GET_ITEM(arg, i);
          Py_INCREF(v);
          res->ob_item[i] = v;
      }
      Py_DECREF(arg);
      for (; i < max_len; ++i) {
          if (dict == NULL) {
              ob = Py_None;
          }
          else {
              ob = _PyDict_GetItemStringWithError(dict,
                  type->tp_members[i-n_unnamed_fields].name);
              if (ob == NULL) {
                  if (PyErr_Occurred()) {
                      Py_DECREF(res);
                      return NULL;
                  }
                  ob = Py_None;
              }
          }
          Py_INCREF(ob);
          res->ob_item[i] = ob;
      }
  
      _PyObject_GC_TRACK(res);
      return (PyObject*) res;
  }
  
  
  static PyObject *
  structseq_repr(PyStructSequence *obj)
  {
      PyTypeObject *typ = Py_TYPE(obj);
      _PyUnicodeWriter writer;
  
      /* Write "typename(" */
      PyObject *type_name = PyUnicode_DecodeUTF8(typ->tp_name,
                                                 strlen(typ->tp_name),
                                                 NULL);
      if (type_name == NULL) {
          return NULL;
      }
  
      _PyUnicodeWriter_Init(&writer);
      writer.overallocate = 1;
      /* count 5 characters per item: "x=1, " */
      writer.min_length = (PyUnicode_GET_LENGTH(type_name) + 1
                           + VISIBLE_SIZE(obj) * 5 + 1);
  
      if (_PyUnicodeWriter_WriteStr(&writer, type_name) < 0) {
          Py_DECREF(type_name);
          goto error;
      }
      Py_DECREF(type_name);
  
      if (_PyUnicodeWriter_WriteChar(&writer, '(') < 0) {
          goto error;
      }
  
      for (Py_ssize_t i=0; i < VISIBLE_SIZE(obj); i++) {
          if (i > 0) {
              /* Write ", " */
              if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0) {
                  goto error;
              }
          }
  
          /* Write "name=repr" */
          const char *name_utf8 = typ->tp_members[i].name;
          if (name_utf8 == NULL) {
              PyErr_Format(PyExc_SystemError, "In structseq_repr(), member %zd name is NULL"
                           " for type %.500s", i, typ->tp_name);
              goto error;
          }
  
          PyObject *name = PyUnicode_DecodeUTF8(name_utf8, strlen(name_utf8), NULL);
          if (name == NULL) {
              goto error;
          }
          if (_PyUnicodeWriter_WriteStr(&writer, name) < 0) {
              Py_DECREF(name);
              goto error;
          }
          Py_DECREF(name);
  
          if (_PyUnicodeWriter_WriteChar(&writer, '=') < 0) {
              goto error;
          }
  
          PyObject *value = PyStructSequence_GET_ITEM(obj, i);
          assert(value != NULL);
          PyObject *repr = PyObject_Repr(value);
          if (repr == NULL) {
              goto error;
          }
          if (_PyUnicodeWriter_WriteStr(&writer, repr) < 0) {
              Py_DECREF(repr);
              goto error;
          }
          Py_DECREF(repr);
      }
  
      if (_PyUnicodeWriter_WriteChar(&writer, ')') < 0) {
          goto error;
      }
  
      return _PyUnicodeWriter_Finish(&writer);
  
  error:
      _PyUnicodeWriter_Dealloc(&writer);
      return NULL;
  }
  
  
  static PyObject *
  structseq_reduce(PyStructSequence* self, PyObject *Py_UNUSED(ignored))
  {
      PyObject* tup = NULL;
      PyObject* dict = NULL;
      PyObject* result;
      Py_ssize_t n_fields, n_visible_fields, n_unnamed_fields, i;
  
      n_fields = REAL_SIZE(self);
      if (n_fields < 0) {
          return NULL;
      }
      n_visible_fields = VISIBLE_SIZE(self);
      n_unnamed_fields = UNNAMED_FIELDS(self);
      if (n_unnamed_fields < 0) {
          return NULL;
      }
      tup = _PyTuple_FromArray(self->ob_item, n_visible_fields);
      if (!tup)
          goto error;
  
      dict = PyDict_New();
      if (!dict)
          goto error;
  
      for (i = n_visible_fields; i < n_fields; i++) {
          const char *n = Py_TYPE(self)->tp_members[i-n_unnamed_fields].name;
          if (PyDict_SetItemString(dict, n, self->ob_item[i]) < 0)
              goto error;
      }
  
      result = Py_BuildValue("(O(OO))", Py_TYPE(self), tup, dict);
  
      Py_DECREF(tup);
      Py_DECREF(dict);
  
      return result;
  
  error:
      Py_XDECREF(tup);
      Py_XDECREF(dict);
      return NULL;
  }
  
  static PyMethodDef structseq_methods[] = {
      {"__reduce__", (PyCFunction)structseq_reduce, METH_NOARGS, NULL},
      {NULL, NULL}
  };
  
  static Py_ssize_t
  count_members(PyStructSequence_Desc *desc, Py_ssize_t *n_unnamed_members) {
      Py_ssize_t i;
  
      *n_unnamed_members = 0;
      for (i = 0; desc->fields[i].name != NULL; ++i) {
          if (desc->fields[i].name == PyStructSequence_UnnamedField) {
              (*n_unnamed_members)++;
          }
      }
      return i;
  }
  
  static int
  initialize_structseq_dict(PyStructSequence_Desc *desc, PyObject* dict,
                            Py_ssize_t n_members, Py_ssize_t n_unnamed_members) {
      PyObject *v;
  
  #define SET_DICT_FROM_SIZE(key, value)                                         \
      do {                                                                       \
          v = PyLong_FromSsize_t(value);                                         \
          if (v == NULL) {                                                       \
              return -1;                                                         \
          }                                                                      \
          if (PyDict_SetItemString(dict, key, v) < 0) {                          \
              Py_DECREF(v);                                                      \
              return -1;                                                         \
          }                                                                      \
          Py_DECREF(v);                                                          \
      } while (0)
  
      SET_DICT_FROM_SIZE(visible_length_key, desc->n_in_sequence);
      SET_DICT_FROM_SIZE(real_length_key, n_members);
      SET_DICT_FROM_SIZE(unnamed_fields_key, n_unnamed_members);
  
      // Prepare and set __match_args__
      Py_ssize_t i, k;
      PyObject* keys = PyTuple_New(desc->n_in_sequence);
      if (keys == NULL) {
          return -1;
      }
  
      for (i = k = 0; i < desc->n_in_sequence; ++i) {
          if (desc->fields[i].name == PyStructSequence_UnnamedField) {
              continue;
          }
          PyObject* new_member = PyUnicode_FromString(desc->fields[i].name);
          if (new_member == NULL) {
              goto error;
          }
          PyTuple_SET_ITEM(keys, k, new_member);
          k++;
      }
  
      if (_PyTuple_Resize(&keys, k) == -1) {
          goto error;
      }
  
      if (PyDict_SetItemString(dict, match_args_key, keys) < 0) {
          goto error;
      }
  
      Py_DECREF(keys);
      return 0;
  
  error:
      Py_DECREF(keys);
      return -1;
  }
  
  static void
  initialize_members(PyStructSequence_Desc *desc, PyMemberDef* members,
                     Py_ssize_t n_members) {
      Py_ssize_t i, k;
  
      for (i = k = 0; i < n_members; ++i) {
          if (desc->fields[i].name == PyStructSequence_UnnamedField) {
              continue;
          }
  
          /* The names and docstrings in these MemberDefs are statically */
          /* allocated so it is expected that they'll outlive the MemberDef */
          members[k].name = desc->fields[i].name;
          members[k].type = T_OBJECT;
          members[k].offset = offsetof(PyStructSequence, ob_item)
            + i * sizeof(PyObject*);
          members[k].flags = READONLY;
          members[k].doc = desc->fields[i].doc;
          k++;
      }
      members[k].name = NULL;
  }
  
  
  int
  _PyStructSequence_InitType(PyTypeObject *type, PyStructSequence_Desc *desc,
                             unsigned long tp_flags)
  {
      PyMemberDef *members;
      Py_ssize_t n_members, n_unnamed_members;
  
  #ifdef Py_TRACE_REFS
      /* if the type object was chained, unchain it first
         before overwriting its storage */
      if (type->ob_base.ob_base._ob_next) {
          _Py_ForgetReference((PyObject *)type);
      }
  #endif
  
      /* PyTypeObject has already been initialized */
      if (Py_REFCNT(type) != 0) {
          PyErr_BadInternalCall();
          return -1;
      }
  
      type->tp_name = desc->name;
      type->tp_basicsize = sizeof(PyStructSequence) - sizeof(PyObject *);
      type->tp_itemsize = sizeof(PyObject *);
      type->tp_dealloc = (destructor)structseq_dealloc;
      type->tp_repr = (reprfunc)structseq_repr;
      type->tp_doc = desc->doc;
      type->tp_base = &PyTuple_Type;
      type->tp_methods = structseq_methods;
      type->tp_new = structseq_new;
      type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | tp_flags;
      type->tp_traverse = (traverseproc) structseq_traverse;
  
      n_members = count_members(desc, &n_unnamed_members);
      members = PyMem_NEW(PyMemberDef, n_members - n_unnamed_members + 1);
      if (members == NULL) {
          PyErr_NoMemory();
          return -1;
      }
      initialize_members(desc, members, n_members);
      type->tp_members = members;
  
      if (PyType_Ready(type) < 0) {
          PyMem_Free(members);
          return -1;
      }
      Py_INCREF(type);
  
      if (initialize_structseq_dict(
              desc, type->tp_dict, n_members, n_unnamed_members) < 0) {
          PyMem_Free(members);
          Py_DECREF(type);
          return -1;
      }
  
      return 0;
  }
  
  int
  PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
  {
      return _PyStructSequence_InitType(type, desc, 0);
  }
  
  void
  PyStructSequence_InitType(PyTypeObject *type, PyStructSequence_Desc *desc)
  {
      (void)PyStructSequence_InitType2(type, desc);
  }
  
  
  void
  _PyStructSequence_FiniType(PyTypeObject *type)
  {
      // Ensure that the type is initialized
      assert(type->tp_name != NULL);
      assert(type->tp_base == &PyTuple_Type);
  
      // Cannot delete a type if it still has subclasses
      if (type->tp_subclasses != NULL) {
          return;
      }
  
      // Undo PyStructSequence_NewType()
      type->tp_name = NULL;
      PyMem_Free(type->tp_members);
  
      _PyStaticType_Dealloc(type);
      assert(Py_REFCNT(type) == 1);
      // Undo Py_INCREF(type) of _PyStructSequence_InitType().
      // Don't use Py_DECREF(): static type must not be deallocated
      Py_SET_REFCNT(type, 0);
  
      // Make sure that _PyStructSequence_InitType() will initialize
      // the type again
      assert(Py_REFCNT(type) == 0);
      assert(type->tp_name == NULL);
  }
  
  
  PyTypeObject *
  _PyStructSequence_NewType(PyStructSequence_Desc *desc, unsigned long tp_flags)
  {
      PyMemberDef *members;
      PyTypeObject *type;
      PyType_Slot slots[8];
      PyType_Spec spec;
      Py_ssize_t n_members, n_unnamed_members;
  
      /* Initialize MemberDefs */
      n_members = count_members(desc, &n_unnamed_members);
      members = PyMem_NEW(PyMemberDef, n_members - n_unnamed_members + 1);
      if (members == NULL) {
          PyErr_NoMemory();
          return NULL;
      }
      initialize_members(desc, members, n_members);
  
      /* Initialize Slots */
      slots[0] = (PyType_Slot){Py_tp_dealloc, (destructor)structseq_dealloc};
      slots[1] = (PyType_Slot){Py_tp_repr, (reprfunc)structseq_repr};
      slots[2] = (PyType_Slot){Py_tp_doc, (void *)desc->doc};
      slots[3] = (PyType_Slot){Py_tp_methods, structseq_methods};
      slots[4] = (PyType_Slot){Py_tp_new, structseq_new};
      slots[5] = (PyType_Slot){Py_tp_members, members};
      slots[6] = (PyType_Slot){Py_tp_traverse, (traverseproc)structseq_traverse};
      slots[7] = (PyType_Slot){0, 0};
  
      /* Initialize Spec */
      /* The name in this PyType_Spec is statically allocated so it is */
      /* expected that it'll outlive the PyType_Spec */
      spec.name = desc->name;
      spec.basicsize = sizeof(PyStructSequence) - sizeof(PyObject *);
      spec.itemsize = sizeof(PyObject *);
      spec.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | tp_flags;
      spec.slots = slots;
  
      type = (PyTypeObject *)PyType_FromSpecWithBases(&spec, (PyObject *)&PyTuple_Type);
      PyMem_Free(members);
      if (type == NULL) {
          return NULL;
      }
  
      if (initialize_structseq_dict(
              desc, type->tp_dict, n_members, n_unnamed_members) < 0) {
          Py_DECREF(type);
          return NULL;
      }
  
      return type;
  }
  
  
  PyTypeObject *
  PyStructSequence_NewType(PyStructSequence_Desc *desc)
  {
      return _PyStructSequence_NewType(desc, 0);
  }
  
  
  /* runtime lifecycle */
  
  PyStatus _PyStructSequence_InitState(PyInterpreterState *interp)
  {
      if (!_Py_IsMainInterpreter(interp)) {
          return _PyStatus_OK();
      }
  
      if (_PyUnicode_FromId(&PyId_n_sequence_fields) == NULL
          || _PyUnicode_FromId(&PyId_n_fields) == NULL
          || _PyUnicode_FromId(&PyId_n_unnamed_fields) == NULL)
      {
          return _PyStatus_ERR("can't initialize structseq state");
      }
      return _PyStatus_OK();
  }
  